1. Field of the Invention
The present invention relates to display devices, and more particularly to a liquid crystal display device and a method for driving the same.
2. Discussion of the Related Art
Because of their characteristic low operation voltage and power consumption, portability, and other advantages, super-thin flat panel displays, and in particular, liquid crystal display devices, have a wide and variety of applications, such as displays for notebook computers, monitors, air crafts, and space crafts.
A typical liquid crystal display device is provided with a liquid crystal display panel, and a driving circuit for driving the liquid crystal display panel. The liquid crystal display panel has a color filter substrate and a thin film transistor substrate bonded together, and a liquid crystal layer injected into a space between the bonded two substrates. The thin film transistor substrate has a plurality of gate lines that cross a plurality of data lines to define a matrix of pixel regions, pixel electrodes each formed on a respective pixel region, and a plurality of thin film transistors each switched in response to a gate line signal for transmitting a data line signal to a pixel electrode. The color filter substrate has a black matrix for that blocks lights incident on portions of the liquid crystal display panel other that the pixel regions, a R, G, B color filter layer for expressing a color, and a common electrode for forming an electric field together with the pixel electrode.
The driving circuit for driving the liquid crystal display panel has a gate driver, a data driver, a timing control unit for controlling the gate driver and the data driver, and a common voltage generating unit for supplying a common voltage to the liquid crystal display panel.
The liquid crystal display device displays an image by using a difference of transmissivities of lights corresponding to an orientation of liquid crystal molecules. The orientation of the liquid crystal molecules is controlled by controlling an electric field between the two substrates of the liquid crystal display panel.
The common voltage generating unit generates a common voltage Vcom by using a voltage of a power source of a DC/DC converting unit at the liquid crystal display panel for driving the liquid crystal display panel. The common voltage Vcom is supplied to the common electrode at the liquid crystal display panel. A parasitic capacitance is formed between the common electrode of the color filter substrate and the data lines of the thin film transistor substrate.
When a data signal value between the data lines changes sharply, the parasitic capacitance causes a ripple at the common voltage Vcom supplied to the common electrode. The ripple distorts the common voltage Vcom, and causes cross talk when the distorted common voltage is supplied to the liquid crystal display panel. To eliminate the cross talk, a common voltage compensating unit is provided for supplying a compensated common voltage to the liquid crystal display panel.
However, the distortion of the common voltage Vcom at a center of the common electrode is different from the distortion of the common voltage Vcom at a periphery of the common electrode of the liquid crystal display panel due to difference of load characteristics and the like. That is, the distortion of the common electrode voltage that occurs in a large area liquid crystal display panel or due to a resistance of the common electrode is different for each portions of the common electrode of the liquid crystal display panel. In particular, the difference in distortion voltage may be great between the center and the periphery.
Consequently, even if the common voltage Vcom compensating unit supplies a compensated common voltage to the liquid crystal display panel, the distortion of the common voltage Vcom can not be overcome due to a variation in the distortion between the center and the periphery.